PST TiAl单晶力学性能与服役行为

Reducing weight is the eternal theme in aeronautic and astronautic industries. The density of TiAl alloys is only 3.9g/cm3, while that of Ni-based superalloys is about 8.5g/cm3. Therefore, the replacement of Ni-based superalloys with TiAl alloys can reduce weight remarkably. However, the room temperature brittlement and low service temperature in TiAl alloys limit their application. Polysynthetic Twinned (PST) TiAl single crystals attain a considerable enhancement in strength, ductility and creep resistance, and increase the temperature at which strength drops drastically from around 650~700℃ to over 950℃, possessing a broad application prospect. In order to fully satisfy the strict performance requirements of aeronautical engine blades, this proposal will focus on the systematic study of structural stability and oxidation resistance of PST TiAl single crystals at elevated temperatures, as well as the in-depth understanding of the creep performance and fatigue behavior under various stress and temperature conditions. Furthermore, our efforts will be focused on disclosing the coarsening, spheroidization and decomposing mechanisms of the lamellars in PST TiAl single crystals. These studies are beneficial for clarifying the underlying mechanisms that control the deformation, crack initiation and crack propagation behaviors in creep and fatigue experiments. A numerical simulation model will be established for the prediction of creep and fatigue life. All these efforts will lead to the accurate assessment of the key mechanical properties as well as the service temperature range, laying the solid foundation for the practical application of PST TiAl single crystals.

减重是航空航天武器装备永恒不变的主题。TiAl合金密度只有3.9，而Ni基高温合金约为8.5，用TiAl合金替代Ni基合金减重效益显著。但TiAl合金室温脆性大和服役温度低两大难题限制了其应用范围。PST TiAl单晶实现了强度、塑性和蠕变抗力的跨越性提升，将强度急降温度由650~700℃左右提高到950℃以上，具有重要应用前景。本项目针对航空发动机叶片服役条件对材料性能的要求，系统研究PST TiAl单晶高温组织稳定性与抗氧化性能、不同温度与应力水平的蠕变行为、高低周疲劳性能等关键力学性能与服役行为。揭示片层粗化、球化及分解机制，探明PST TiAl单晶高温蠕变变形和断裂机理、疲劳裂纹萌生/扩展过程和机理，建立蠕变和疲劳寿命预测方法与模型，准确评价关键力学性能，界定可以安全使用的服役温度范围，为PST TiAl单晶的实际应用奠定坚实基础。

本项目针对航空发动机叶片服役条件对材料性能的要求，系统研究了PST TiAl单晶高温组织稳定性与抗氧化性能、不同温度与应力水平的蠕变行为、室温~1000℃疲劳性能等关键力学性能与服役行为。准确评价了PST TiAl单晶700~1000℃高温长时组织稳定性、抗氧化性能、蠕变和疲劳等关键力学性能，界定了PST TiAl单晶可以安全使用的长时服役温度范围；揭示了PST TiAl单晶高温长时组织退化机制为位移-扩散型相变控制的α2片层溶解，和原子短程扩散控制的120°旋转有序畴界迁移；建立了PST TiAl单晶恒温氧化动力学方程，探明了均匀腐蚀行为；发明了PST TiAl单晶抗氧化TiAlCrY涂层，阐明了Cr、Mo扩散阻挡层对TiAl/NiCrAlY涂层界面稳定性的影响规律；建立了PST TiAl单晶蠕变时间-应变量-蠕变速率曲线，阐释了表面氧化层诱导裂纹萌生和扩展的蠕变断裂机制；建立了PST TiAl单晶疲劳S-N曲线，发现软/硬片层塑性应变离域化可以显著提高疲劳性能，提出了考虑机器学习的蠕变寿命预测方法和考虑应力水平的高周疲劳寿命预测方程；发现PST TiAl单晶与已报道的所有片层材料不同的断裂行为，提出了片层材料RT判据。研究成果对轻质耐热合金以及片层材料研究具有借鉴意义，为PST TiAl单晶的实际应用奠定了坚实基础。.本项目中期完成情况综合评分为优秀。研究成果由国家自然科学基金委员会2022年简报第7期分送中共中央办公厅、全国人大常委会办公厅、国务院办公厅、全国政协办公厅，荣获2021年度国防科技进步一等奖，被评为年度十大科技进展。

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